What learning really matters for today's learners? In this article, David N. Perkins promises not to provide the answer, but rather to consider how we might think about the question. Learning that matters--which he calls lifeworthy learning--is characterized by four earmarks: opportunity, insight, action, and ethics. Educators should ask themselves, Is the learner likely to have many opportunities to use this learning throughout life? Does it offer important insights? Will it affect the learner's actions? And does it provide an ethical perspective? The good news is that the familiar academic disciplines offer a rich harvest of big understandings that are lifeworthy. The problem is that instruction often focuses instead on niche understandings--those that have little reach beyond the technical particulars of the discipline. Cell mitosis, a staple of high school biology classes, is a good example: Perkins asserts that learning the details of this process has less import than exploring more lifeworthy biology topics, such as the nature of communicable diseases or the ethical questions around genetic engineering. Students who have specific interests and passions should be able to develop expertise, but for most students, "the fundamentals, robustly understood and widely applied, are what deliver the greatest payoff."